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The effect of load weight vs. pace on muscle recruitment during lifting.

The purpose of this study was to compare the effect on the trunk and upper extremity muscle recruitment when controlling the lifting pace and the lifting weight. Thirty nine healthy subjects performed a total of 12 lifts (3 lifting trials per condition, 2 lifting weights, and 2 lifting paces), from waist height to shoulder height. Kinematics of upper extremity and the box and electromyography of trunk and upper extremity muscles were collected. Temporal muscle recruitment pattern varied between muscles based on their function. Heavier lifting weight evenly increased the muscle recruitment throughout the lifting period without changing their temporal pattern. In contrary, lifting pace affected the temporal recruitment pattern in most of muscles. The faster lifting pace increased the muscle recruitment at the beginning phase but decreased at the terminal phase of lifting. It is important to educate the workers about the effect of lifting pace and weight on the biomechanical load to control the mechanical load on the muscles and spine.